This application is related to Korean Patent Application No. 99-14763, filed Apr. 23, 1999, and takes priority from that date.
1. Field of the Invention
The present invention relates to an organic anti-reflective coating material which allows the stable formation of ultrafine patterns suitable for 64M, 256M, 1 G, 4 G and 16 G DRAM semiconductor devices. More particularly, the present invention relates to an organic anti-reflective coating material which contains a chromophore with high absorbance at the wavelengths useful for submicrolithography. A layer of said anti-reflection material can prevent back reflection of light from lower layers or the surface of the semiconductor chip, as well as eliminate the standing waves in the photoresist layer, during a submicrolithographic process using a 248 nm KrF, 193 nm ArF or 157 nm F2 laser light sources. Also, the present invention is concerned with an anti-reflective coating composition comprising such a material, an anti-reflective coating therefrom and a preparation method thereof.
2. Description of the Prior Art
During a submicrolithographic process, one of the most important processes for fabricating highly integrated semiconductor devices, there inevitably occur standing waves and reflective notching of the waves due to the optical properties of lower layers coated on the wafer and to changes in the thickness of the photosensitive film applied thereon. In addition, the submicrolithographic process generally suffers from a problem of the CD (critical dimension) being altered by diffracted and reflected light from the lower layers.
To overcome these problems, it has been proposed to introduce a film, called an anti-reflective coating (hereinafter sometimes referred to as xe2x80x9cARCxe2x80x9d), between the substrate and the photosensitive film. Generally, ARCs are classified as xe2x80x9corganicxe2x80x9d and xe2x80x9cinorganicxe2x80x9d depending on the materials used, and as xe2x80x9cabsorptivexe2x80x9d and xe2x80x9cinterferingxe2x80x9d depending on the mechanism of operation. In microlithographic processes using I-line (365 nm wavelength) radiation, inorganic ARCs, for example TiN or amorphous carbon coatings, are employed when advantage is taken of an absorption mechanism, and SiON coatings are employed when an interference mechanism is employed. The SiON ARCs are also adapted for submicrolithographic processes which use KrF light sources.
Recently, extensive and intensive research has been and continues to be directed to the application of organic ARCs for such submicrolithography. In view of the present development status, organic ARCs must satisfy the following fundamental requirements to be useful:
First, the peeling of the photoresist layer due to dissolution in solvents in the organic ARC should not take place when conducting a lithographic process. In this regard, the organic ARC materials have to be designed so that their cured films have a crosslinked structure without producing by-products.
Second, there should be no migration of chemical materials, such as amines or acids, into and from the ARCs. If acids are migrated from the ARC, the photosensitive patterns are undercut while the egress of bases, such as amines, causes a footing phenomena.
Third, faster etch rates should be realized in the ARC than in the upper photosensitive film, allowing an etching process to be conducted smoothly with the photosensitive film serving as a mask.
Finally, the organic ARCs should be as thin as possible while playing an excellent role in preventing light reflection.
Despite the variety of ARC materials, those which are satisfactorily applicable to submicrolithographic processes using ArF light have not been found, thus far. As for inorganic ARCs, there have been reported no materials which can control the interference at the ArF wavelength, that is, 193 nm. As a result, active research has been undertaken to develop organic materials which act as superb ARCs. In fact, in most cases of submicrolithography, photosensitive layers are necessarily accompanied by organic ARCs which prevent the standing waves and reflective notching occurring upon light exposure, and eliminate the influence of the back diffraction and reflection of light from lower layers. Accordingly, the development of such an ARC material showing high absorption properties against specific wavelengths is one of the hottest and most urgent issues in the art.
U.S. Pat. No. 4,910,122 discloses an ARC which is interposed under photosensitive layers to eliminate defects caused by reflected light. The coating described therein can be formed thinly, smoothly and uniformly and includes a light absorbing dye which eliminates many of the defects caused by reflected light, resulting in increased sharpness of the images in photosensitive materials. These types of ARCs, however, suffer from disadvantages of being complicated in formulation, extremely limited in material selection and difficult to apply for photolithography using Deep Ultraviolet (DUV) radiation. For example, the ARC of the above reference comprises 4 dye compounds, including polyamic acid, curcumin, Bixin and Sudan Orange G, and 2 solvents, including cyclohexanone and N-methyl-2-pyrrolidone. This multi-component system is not easy to formulate and may intermix with the resist composition coated thereover, bringing about undesired results.
Therefore, it is an object of the present invention to overcome the problems encountered in the prior art and to provide a novel organic compound which can be used as an ARC for submicrolithography using 193 nm ArF, 248 nm KrF and 157 nm F2 lasers.
It is another object of the present invention to provide a method for preparing an organic compound which prevents the diffusion and reflection caused by the light exposure in submicrolithography.
It is a further object of the present invention to provide an ARC composition containing such a diffusion/reflection-preventive compound and a preparation method therefor.
It is a still further object of the present invention to provide an ARC formed from such a composition and a preparation method therefor.
The present invention pertains to acrylate polymer resins which can be used as an ARC. Preferred polymer resins contain a chromophore which exhibits high absorbance at 193 nm and 248 nm wavelengths. A crosslinking mechanism between alcohol groups and other functional groups is introduced into the polymer resins, so that a crosslinking reaction takes place when coatings of the polymer resins are xe2x80x9chard bakedxe2x80x9d, thereby greatly improving the formation, tightness and dissolution properties of the ARCs. In particular, optimum crosslinking reaction efficiency and storage stability are realized in the present invention. The ARC resins of the present invention show superior solubility in all hydrocarbon solvents, but are of so high solvent resistance after hard baking that they are not dissolved in any solvent at all. These advantages allow the resins to be coated without any problem, and the coating prevents the undercutting and footing problems which can occur upon forming images on photosensitive materials. Furthermore, the coatings made of the acrylate polymers of the present invention are higher in etch rate than photosensitive films, improving the etch selection ratio therebetween.
The ARC resins of the present invention are selected from the group consisting of acrylate polymers represented by the following general formulas I, II and III: 
wherein,
R, RI, RII, and RIII are independently hydrogen or a methyl group;
R0 is a methyl group or an ethyl group;
R1 to R9, which are the same or different, each represents hydrogen, hydroxy, methoxycarbonyl, carboxyl, hydroxymethyl, or a substituted or unsubstituted, linear or branched C1-C6 alkyl, alkane, alkoxyalkyl or alkoxyalkane;
x, y and z each is a mole fraction in the range from 0.01 to 0.99; and
m and n are independently an integer of 1 to 4. In a preferred compound of Formula I, m is 1 or 2 and n is an integer of 1 to 4. In a preferred compound of Formula II, m is 1 or 2 and n is an integer from 2 to 4.
The polymers of the present invention are designed to provide greater absorbance at 193 nm and 248 nm wavelengths. To accomplish this result, a chromophore substituent which is able to absorb light at a wavelength of 193 nm as well as 248 nm is grafted to the backbone of the polymer.
The polymer of the general formula I, as illustrated in the following reaction formula 1, can be prepared by polymerizing 9-anthracenemethyl acrylate type monomers (I) and hydroxy alkylacrylate type monomers (II) with the aid of an initiator in a solvent. Each of the monomers has a mole fraction ranging from 0.01 to 0.99. 
wherein R, RI, R1 to R9, x, y, m and n each is as defined above.
The polymers of the general formula II can be prepared in a similar manner to the polymers of the general formula I, using 9-anthracenemethyl acrylate type monomers (I), hydroxy alkylacrylate type monomers (II) and methylmethacrylate monomers (III) at a mole fraction of 0.01 to 0.99 for each monomer, as illustrated in the following reaction formula 2: 
wherein R, RI, RII, R1 to R9, x, y, z, m and n each is as defined above.
The preparation of the polymer of the general formula III is illustrated in the following reaction formula 3. As shown, first, methacryloyl chloride (IV) is reacted with 4-hydroxy benzaldehyde (V) to give 4-formylphenylmethacrylate (VI) which is then polymerized with the aid of an initiator in a solvent, followed by substituting the 4-formylphenyl groups with methanol or ethanol: 
wherein RIII and R0 each is as defined above.
For initiating the polymerization reaction for the polymers of the general formulas I, II and III, ordinary initiators may be used, with preference given to 2,2-azobisisobutyronitrile (AIBN), acetylperoxide, laurylperoxide and t-butylperoxide. Also, ordinary solvents may be used for the polymerization. Preferably the solvent is selected from the group consisting of tetrahydrofuran, toluene, benzene, methylethyl ketone and dioxane.
Preferably, the polymerization of the polymers of the general formulas I and II is carried out at 50-90xc2x0 C.
The 9-anthracene alkyl acrylate type monomers (I) used to prepare the polymers of the general formulas I and II, are novel compounds which can be prepared by the reaction of 9-anthracene alcohol with acryloyl chloride type compounds in a solvent, as illustrated in the following reaction formula 4: 
wherein R, R1 to R9, and n each is as defined above. The hydroxyalkylacrylate type monomers (II) and methylmethacrylate monomers (III) used in the above reactions are commercially available, or they may be prepared using known preparation methods.
Also, the present invention pertains to an ARC composition which is based on a polymer mixture comprising the polymer of the general formula I or II and the polymer of the general formula III, in combination with at least one additive selected from the group consisting of the anthracene derivatives shown in Table 1, below.
In Table 1, R11, R12, R13, R14 and R15 independently represent hydrogen, hydroxy, hydroxymethyl, or substituted or unsubstituted linear or branched C1-C5 alkyl, alkane, alkoxyalkyl or alkoxyalkane.
ARC compositions according to the present invention may be prepared by (i) dissolving a polymer of the general formula I or II and a polymer of general formula III in a solvent to form a solution; (ii) optionally adding a compound selected from Table 1 to said solution, at an amount of 0.1 to 30% by weight, and (iii) filtering the solution.
Ordinary organic solvents may be used in preparing the composition, with preference given to ethyl 3-ethoxypropionate, methyl 3-methoxy propionate, cyclohexanone and propylene methyletheracetate. The solvent is preferably used at an amount of 200 to 5000% by weight based on the total weight of the ARC resin polymers used.
In another aspect of the present invention, an ARC is formed from the coating composition described above. After being filtered, this coating composition may be applied on a wafer in a conventional manner and then xe2x80x9chard-bakedxe2x80x9d (i.e., heated to a temperature of 100-300xc2x0 C. for 10-1000 seconds) to form a crosslinked ARC. Quality semiconductor devices can be fabricated using ARCs of the present invention, because this crosslinked structure of the ARC offers optically stable light exposure conditions when forming an image in the photosensitive layer.
It has been found that the ARCs of the present invention exhibit high performance in submicrolithographic processes using 248 nm KrF, 193 nm ArF and 157 nm F2 lasers as light sources. The same was also true when 157 nm E-beams, EUV extreme ultraviolet) and ion beams are used as light sources.